The present invention relates to a suction system in an engine, and more particularly to a suction system provided with a suction air volume detecting means for use in an automotive engine.
Hitherto, one type of suction air volume detecting means in an automotive engine, as disclosed e.g. in Japanese Laid-Open Patent Publication No. 130718/1976 (corresponding to U.S. Pat. No. 3,956,928) which uses von Karman's vortex flowmeter principle has been proposed. However, in order for the von Karman's vortex flowmeter to operate stably it is indispensable that the von Karman's vortex generated by generating elements be generated regularly and stably. However, as well known in the art, the air to be sucked into an automotive engine undergoes a strong pulsation, and, in particular, the pulsation of the suction air is severest near the full opening of the throttle valve in a four cycle internal combustion engine, i.e. near its full load condition so that the von Karman's vortexes are greatly affected, making the vortex generation unstable, resulting in errors in the detected volume of the suction air.
One patent showing the state of art having a relatively close connection with the present invention is U.S. Pat. No. 3,722,275 issued on Mar. 27, 1973 which discloses a blunt body flowmeter arrangement for use in controlling air pollution produced by internal combustion engines. Although this flowmeter resembles a von Karman's air flowmeter to which the present invention relates, in principle, the former is exclusively used for monitoring the air intake of the combustion engine for the purpose of controlling the atmospheric pollution by such engines, but this patent does not disclose the flowmeter in combination with an air cleaning chamber and an expansion chamber as in the present invention.